This invention relates to pump apparatus for biomedical use and in particular but not exclusively for use in intravenous infusion of liquids to the human body or animal body.
Many medical procedures require the controlled introduction of liquids over a prolonged period into the human or animal body for example where a patient is to receive a drug, blood products, saline or nutrients etc at a controlled dose rate. Existing pump apparatus for such applications includes syringe pumps, drip monitors and peristaltic pumps each of which suffer the disadvantages of being expensive, complex to set up and operate and are generally inhibiting of patient movement. It is also known to introduce liquids into plants in a controlled manner in situations where it is inconvenient to have complex pump apparatus relying on external power supplies.
It has also been proposed in DE-2920975 for example to have a peristaltic pump within a housing which also contains means for controlling and actuating the pump so that the apparatus is self-contained and portable and may for example be attached to the body receiving an infusion.
A disadvantage of such peristaltic pumps is that the rate of flow at which liquid is delivered by the pump cannot be accurately controlled. Typically flow rate is measured by counting revolutions of the peristaltic roller mechanism and errors of up to 15% are typical in measured flow rate. A further difficulty is that, in the event of occlusion of the infusion flow path, known pumps and particularly syringe pumps are generally capable of building-up liquid pressure to a dangerous level. It is also difficult to effectively detect the presence of air bubbles within known pumps and typically a bubble detector relies on the use of sensors responsive to the difference in refractive index between air and the liquid being pumped. The presence of air bubbles is extremely dangerous during infusion and a disadvantage of known pumps is that any air bubble will easily pass through the pump.
It is also known from U.S. Pat. No. 4,596,575 to provide an implantable pump apparatus in which a pump chamber has a flexible wall movable by actuation of a piezoelectric transducer, the chamber having inlet and outlet valves which are electromagnetically actuated poppet valves. The pump is used to pump a buffer fluid which in turn pressurises a bag containing infusate. The infusate therefore does not pass through the pump chamber and the problems associated with bubble formation within the chamber are dealt with by ensuring that the buffer fluid is de-aerated before filling.